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Longitude by Lunars

"Lunar Distances" or lunars for short were used to determine longitude at sea in the period from about 1767 until 1850 (and rarely after that date). This was a time when chronometers were not yet widely available at a reasonable price and were considered unreliable on long voyages. The principle behind lunars is simple. The Moon in the sky is the hour hand of a great clock. The stars along its path are the numbers on the face of the clock. If we can measure the Moon's position relative to the stars, we can read the time from the clock. Comparing that absolute time with local time, usually determined by a time sight, we have our longitude. A one hour difference in time corresponds to a 15 degree difference in longitude.

Comments:


Mark Coady wrote:
I have now done every course I think that has been offered so far at Mystic Seaport taught by Frank Reed in the last two years. I found the courses to all be extremely rewarding.

Several things stand out. The course material is presented in a balanced way, with a well thought mixture of detailed calculation, broken up by historical, factual, and hands-on aspects. This type of teaching is well suited to most, as it provides periods of more intense reasoning with relaxation and humor. Anyone can walk away with new-found knowledge. I also feel that the approach of understanding historical context and a simple practical approach is unique. It has gone a great way toward clearing up a lot of my preconceived ideas and confusions resulting from the many contradictory or esoteric approaches found in various volumes or on the internet.

Very simply, I learned a lot and it went a long way toward clearing up a mess. I was fascinated the whole time. The courses and NavList provide the tools to keep learning even after the course is over. I left able to measure what I see with a more calibrated eye for real world application, and a greater appreciation of human history. I can strongly recommend these classes for the curious, the fascinated, the historian, the hardcore navigator, or the armchair one. There is something in them for all.

I also found the NavList community to be helpful and encouraging as my journey continues. I hope I can undertake even more material in additional courses in the future.

"There is nothing - absolutely nothing - half so much worth doing as simply messing about in boats" (Kenneth Grahame, from the "Wind in the Willows")

Capt. Mark

John Carbone wrote:
Celestial Navigation Courses with Frank Reed ... As a formal naval officer navigator, navigator on Bermuda passages, and many celestial courses, I highly recommend Frank Reed in any course or program he teaches. I have taken his celestial courses at Mystic Seaport, online and followed his engaging web community (NavList.net). Every encounter has been different and educational. With his expertise and polished presentations, you will learn and understand the theory and practice celestial navigation. Frank is the consummate professor and someone not to be missed.
Dr. Stanley J. Zawada & Ilona M. Kovacs wrote:
If we could leave 5 stars, we'd leave 10 ! We have attended several courses and enjoyed each one! Mr. Frank Reed is as entertaining as is his complete mastery of the subjects he teaches. The level of preparedness shines like the stars he so loves. We thank you for the most excellent courses we have had the ultimate pleasure to experience.

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